1. Field of the Invention
The present invention is directed to improved clay/organic chemical compositions that are made from clay and a specified mixture of organic materials. The compositions can be added to a wide variety of polymer, plastic and resin matrices to form inventive nanocomposite materials of enhanced structural strength. They can also be used as rheological additives.
2. Background of the Invention
Organically modified clays, also called organoclays, have been used for many years as rheological additives for solvent based systems. They are usually produced by making a water dispersion of a phyllosilicate clay, usually a smectite clay, and adding to it a quaternary ammonium salt of a long chain fatty acid to produce an organically modified clay by cation exchange reaction and adsorption. The reaction may cause the organoclay to coagulate from the water dispersion which allows for its isolation by filtration and washing. Similarly, organoclays can be made without water by extrusion mixing, with heat and shear, smectite clay and the quaternary ammonium compound or compounds with no water or other solvent being present. This process usually produces an organoclay of lower quality however, since, among other reasons, the final product still has salt reaction byproducts that cannot be washed or readily isolated from the organoclay and for other reasons.
Polymers, resins and plastics containing clay additives have recently become widely used as replacements for heavier steel and other metal products, especially in the field of automotive manufacturing. They have also found use in a growing number of other areas including as bridge components and as replacements for heavier steel parts in ship construction. Using extrusion and injection molding, a nylon matrix, for example, has been successfully reinforced with smectite-type clays (and organoclays based on the smectite clays, bentonite and hectorite) dispersed therein to form molecular composites of nylon and finely dispersed silicate clay platelet layers. Such products, often called nanocomposites, have enhanced structural, tensile, impact and flexural strength.
The behavior of the resultant plastic/clay product (or nanocomposite) is qualitatively different from that exhibited by the plastic, polymer or resin alone and has been attributed by some workers in the field to the confinement of the matrix chains between the clay""s millions of microscopic layers. It has long been known that bentonite and hectorite are clays which are composed of flat silicate platelets of a thickness no more than about one nanometer.
The nanocomposite products created to date have important commercial applications not only in the synthesis and properties of organic/inorganic nano-structure as discussed above but also in diverse areas such as where ultrathin polymer films confined between adsorbed surfaces are involved. These uses include polymer composites for polymer adhesives and films including polyethylene.
The clays used are typically smectite clays which are layered phyllosilicates. Smectite clays possess some structural characteristics similar to the more well-known minerals talc and mica. Their crystal structures consist of two-dimensional layers formed by fusing two silica tetrahedral sheets to an edge-shared dioctahedral or trioctahedral sheet of either alumina (for example bentonite) or magnesia (for example hectorite)xe2x80x94each of the different smectite clays having somewhat different structures. Stacking of these layers in nature in depths of hundreds or more caused by ionic and weak Van der Waals forces leads to voids or chambers between the separate layers. These chambers are occupied by cations which balance the charge deficiency that is generated by isomorphous substitution (often called disharmonies) within the platelet lattices.
Nanocomposites are most often prepared today using organically modified silicates or organoclays produced by a cation exchange reaction between the silicate and an alkylammonium salt (usually quaternary ammonium compounds). The alkyl cations exchanged onto the natural clay platelets render the hydrophilic clay organophilic and this transformation makes the clay more easily dispersible into the polymer or plastic. Although excellent sorbents for some organics, natural bentonite and hectorite are themselves very hydrophilic.
3. Description of the Prior Art
The earliest scientific work using organoclays in the preparation of nanocomposites is reflected in U.S. Pat. No. 2,531,396, issued to a predecessor of Rheox, Inc., the assignee of this invention. This patent filed in 1947 teaches the use of organically modified bentonites to provide structural reinforcement to elastomers, such as rubber, polychloroprene and polyvinyl compounds. Over a generation later, additional patents begin to appear. A number of patents obtained by Toyota starting in 1984: U.S. Pat. Nos. 4,472,538; 4,739,007; 4,810,734; 4,889,885; and 5,091,462 use organoclay additives for plastics and describe plastic structures commercially used, for example, to replace steel components in automobiles.
While not related to nanocomposites, Rheox, Inc. has issued patents describing organoclay compositions useful as rheological additives which comprise the reaction product of smectite clay, quaternary ammonium compounds and organic anions wherein a quaternary-organic anion complex is intercalated with the smectite clayxe2x80x94see for example U.S. Pat. No. 4,412,018xe2x80x94organic anions are described to include a large variety of organic compounds including carboxylic acids, capable of reacting with the quaternary used.
Manufacture to date of nanocomposite materials has often involved mixing an organoclay with a polymer powder, pressing the mixture into a pellet, and heating at the appropriate temperature. For example, polystyrene has been intercalated by mixing polystyrene with an alkylammonium montmorillonite and heating in vacuum. Temperature of heating is chosen to be above the bulk glass transition temperature of polystyrene ensuring polymer melt.
Representative U.S. Pat. No. 4,810,734 to Toyota describes a different process for producing a composite material which comprises a step of contacting a layered smectite clay mineral having a cation exchange capacity of up to 200 milliequivalents per 100 g with a swelling agent in the presence of a dispersion medium, thereby forming a complex which has the property of being swollen by a molten monomer of a polymer, and a polymerization step of polymerizing said monomer in said mixture. The xe2x80x9cswelling agentxe2x80x9d used is one which has both an onium ion and a functional group capable of reacting with a polymer. Toyota U.S. Pat. No. 4,889,885 describes a composite material, which comprises (a) at least one resin selected from the group consisting of a vinyl-based polymeric compound, a thermosetting resin and a rubber, and b) a layered bentonite uniformly dispersed in the resin, the layered silicate having a layer thickness of about 7 to 12 xc3x85 and an interlayer distance of at least about 30 xc3x85, where at least one resin is connected to a layered silicate through an intermediate.
There are a number of ECC America patents issued starting around 1987 where gaseous NH3 is used to provide modification of the smectite clay surfaces prior to making a nanocompositexe2x80x94See U.S. Pat. No. 4,690,868 and 4,798,766.
Two other major companies appear to be working in the field; Amcol International Corporation and AlliedSignal. Both have issued recent patents in the area of this invention. See for example AlliedSignal""s U.S. Pat. Nos. 5,514,734 and 5,385,776xe2x80x94these patents are in general directed toward a nylon 6 matrix and clays using non-standard organic modifications. See also in this regard Vaia et al., the article entitled Synthesis and Properties of Two-Dimensional Nano Structures By Direct Intercalation of Polymer Melts in Layered Silicates, Chemical Materials 1993, 5, pages 1694-1696.
Amcol International Corporation (Amcol) has been issued as least three recent patents, U.S. Pat. Nos. 5,552,469, 5,578,672 and 5,698,627 which teach the exclusion from their clay-based nanocomposites of xe2x80x9conium ionxe2x80x9d products (which would include most known commercial organoclays made with traditional quaternary ammonium compounds). See also Amcol U.S. Pat. No. 5,721,306.
Several patents of the Cornell Research Foundation have issuedxe2x80x94U.S. Pat. No. 5,032,546, 5,032,547 and 5,554,670. One or more of these patents describe the use of organoclays made by the Southern Clay Corporation, Texas.
General Electric Company U.S. Pat. No. 5,530,052 describes silicate materials, including montmorillonite clays, modified with at least one heteroaromatic cation and used as additives to specified polymers to make nanocomposites.
Other prior art shows making polymer-clay intercalates directly by reaction of the monomers in the presence of clays. See Interfacial Effects On The Reinforcement Properties Of Polymer Organoclay Nanocomposites, H Shi, T Lan, T H Pinnavaia, Chemistry of Materials, 1996; pages 88 et seq.
Many of the products described in the prior art references described above have the problem that they are either easy to process and isolate, but are difficult to disperse in a matrix, or they have improved dispersing characteristics but are inconvenient to isolate when manufactured. Traditional organoclays manufactured from quaternary salts and smectite clays are easy to isolate and wash because the reaction of onium salts with ion-exchangeable clays form hydrophobic materials in water that can be conveniently filtered. These materials, however, do not have good compatibility with certain plastic materials.
Water soluble polymer-clay intercalates as described in U.S. Pat. No. 5,552,469, for example, can have good compatibility with polymer, resin and plastic materials but to isolate the additive, one must boil off residual water in an energy intensive fashion. This process also has the potential to leave behind unintercalated polymer along with the clay-polymer intercalate for which there is no simple way of removal. Making a clay-monomer composition with subsequent polymerization can give a well dispersed system in the polymer. Unfortunately, this technique requires that an expensive polymerization train be dedicated to the process and plant contamination with clay can become an issue.
What has escaped scientists is an inexpensive way to make an organic/clay composition that can easily and economically be isolated in high purity and also can be simply processed into a polymer, plastic or resin matrix to form a nanocomposite.
It is an object of the invention to provide a clay/organic chemical composition (which we also call a hybrid organoclay) that can be readily dispersed in plastic and polymer materials to make nanocomposites of improved structural strength.
It is a specific object of the invention to provide such a clay/organic chemical composition that can be readily made and provide use as a rheological additive.
It is a still further object of the invention to provide an inexpensive process to make the clay/organic chemical composition in a manner that can be isolated readily.
This invention is of a clay/organic chemical composition that consists of an organic chemical/smectite clay intercalate that has been ion-exchanged and reacted with one or more quaternary ammonium compounds. This composition is designated as a hybrid organoclay. Since such a hybrid organoclay is hydrophobic, it can be washed with water after manufacture to remove reaction salts and excess water soluble or water dispersible organic material to give a clean product via inexpensive means such as filtration. This allows a better dispersing composition to be prepared without the difficulties of isolation presented by prior art, which uses energy intensive means to remove the bulk of the water from the final product and cannot be easily washed.
In one aspect, the present invention provides a clay/organic chemical composition that comprises: (a) one or more smectite clays, (b) one or more quaternary ammonium compounds which react via an ion exchange mechanism with the clay, and (c) one or more defined non-anionic organic materials that are intercalated with the smectite clay.
Further advantages and features of the invention, as well as the scope, nature and utilization of the invention, will become apparent to those of ordinary skill in the art from the description of the preferred embodiment of the invention set forth below.